Industrial process control systems are used to monitor and control industrial processes that produce or transfer fluids or the like. In such systems, it is typically important to measure “process variables” such as temperatures, pressures, flow rates, level, etc. Process control sensors and transmitters measure and transmit process variables and information related to the measured process variable back to a central location such as a central control room. Additionally, some process variable transmitters may transmit information to other process devices as well.
Examples of process variable measurement include process fluid pressure measurement, process fluid flow measurement, process fluid temperature measurement, process fluid level measurement, etc. The sensors of such devices are typically exposed to a process fluid (liquid or gas) such that a relevant parameter can be measured and transmitted to a monitoring and/or control system in order to effect process control. While providing accurate and precise measurements of the process variables is important for effective for process control, a more basic requirement is that the process fluid itself must not escape. Thus, the process variable measurement point should not generate any leaks in the process installation. Moreover, it is also important that maintenance personnel, tasked to maintain such process devices, not be exposed to hazards as they perform their maintenance activities.
In many industrial process measurement applications, seals are required in order to prevent process fluid leaks. A seal, or pressure barrier, is a mechanical structure that contains process fluid in order to ensure the safety of plant personnel. As such, primary seals or pressure barriers are very important for a process fluid measurement system. In order to provide a safe and robust system, some applications require redundant seals or pressure barriers in order to ensure the safety of plant personnel in the event of failure of a primary seal. Thus, if the primary seal (such as a thermowell) fails, the process fluid will still be contained by a secondary seal or pressure barrier.